Tansforming Deserts Into Forests

The Sahara Forest Project combines two proven technologies in a new way to create multiple benefits: producing large amounts of renewable energy, food and water as well as reversing desertification. A major element of the proposal is the Seawater Greenhouse; a brilliant invention that creates a cool growing environment in hot parts of the world and is a net producer of distilled water from seawater. The Sahara is used here as a metaphor for any desert that formerly supported vegetation and could do so again, given sufficient water.

The second technology, Concentrated Solar Power (CSP) involves concentrating the sun’s heat to create steam that drives conventional turbines, producing zero carbon electricity twice as efficiently as photovoltaics. The two technologoes have very promising synergies that make the economic case even more attractive.

Since the 1980’s, rainfall has increased in several regions, while drying has been observed in the Sahel, the Mediterranean, southern Africa, Australia and parts of Asia. In his report for the Fourth World Conference on the Future of Science “Food and Water for Life” held in Venice last September, Charlie Paton put it this way: The Sahara Forest Project aims to provide a new source of fresh water, food and renewable energy in hot, arid regions, as well as providing conditions that enable re-vegetating areas of desert. The Sahara is used here as a metaphor for any desert that formerly supported vegetation and could do so again, given sufficient water.

This ambitious proposal combines two established technologies – the Seawater Greenhouse and Concentrated Solar Power (CSP) – to achieve highly efficient synergies. Both processes work optimally in sunny, arid conditions. Demonstration plants are already running in Tenerife, Oman and the United Arab Emirates. The estimate that building 20 hectares of greenhouses combined with a 10MW CSP project would cost around $104 million, (€80m) (£65m).

How It Works

To begin, seawater is drawn into each greenhouse complex and dripped over evaporators to be turned into vapor, creating a warm, humid environment poised for growing plants. More water suspended in the air reduces the amount of fresh water needed for direct irrigation. When the air is cycled through the greenhouse to bring more carbon dioxide to the plants, the humid air is released back into the atmosphere and adds moisture to the local environment. The design team proposes that with enough acreage, it may contribute enough added moisture to induce local rainfall.

The evaporators find their necessary power from Concentrated Solar Power (CSP) arrays stretched out across the landscape. Using mirrors to focus sunlight and heat liquid for steam production, CSP is viewed by many as the most viable source of renewable energy in the near term. It can be twice as efficient as photovoltaic panels in energy production as it uses the sun’s energy to create power. The system also produces a great deal of waste heat.

By themselves, these two systems are impressive technologies with a great deal of potential, but linked and integrated together, their possibilities rise exponentially. The excess heat of the CSP facilities can be captured through cogeneration and used for the desalination of more saltwater. The project team estimates that onsite power can desalinate 40 million cubic meters of water for terawatt-hour of harvested solar power—that is over 10.5 billion gallons. Strips of greenhouses can be arranged to shield the CSP mirror arrays and reduce dust and sand collection that lowers their efficiency. Three new export streams can emerge from each project location, all of which are in extreme demand around the globe: clean power, fresh water, fresh food.

Cyclical Progress

As with any good system built on ecological underpinnings, its function begets its own continued success. Theoretically, as the installations grow in size and number more sand is replaced with greenhouses or planted fields. Moisture content in the air will continue to rise while the ground temperature of more acres will continue to fall. The expansion of deserts could be reversed to eventually re-vegetate some of the world’s harshest climates turning them into net producers of vital resources.

While the project is an impressive map for a regenerative, progressive model, I think that the possibilities go even further.

• Plant waste from greenhouses is rich in nutrients and can be composted to produce a base for naturally fertilizing future crops or spread over surrounding area to instigate new native plant growth.
• Another possibility is taking a page from the city of Kalundborg’s playbook and using the wealth of heated salt water for fish farming. This could produce yet another food crop and another organic waste stream that can be used to create organic fertilizers.
• So much desalination will also produce a great deal of salt, which draws us back to CSP. One of the reasons CSP seems so promising is the opportunity for power storage with heated salt solutions being one of the frontrunners. Eventually, excess power could be sold day and night to surrounding townships.

So what’s the catch? Well how much it costs to build solar greenhouses, CSP arrays and the labor to manage them all has to factor in somehow and chart a realistic time frame for expansion. There is also the fact that the Sahara is the world’s largest desert (3.3 million square miles) and constitutes nearly a quarter of Africa. Such statistics begs the question of how many facilities would have to be created before the stated goal of local climate alteration was actually achieved. The number could be staggering.

• References >>
• http://progressivetimes.wordpress.com
• http://www.forcedgreen.com
• http://www.popsci.com